The intensity of an x-ray which is absorbed and/or scattered by a body region of a patient to be examined is measured in a computed tomograph (CT) in various individual image recordings and a three-dimensional volume model of the body region to be examined is subsequently produced from the individual image recordings. To record the individual images, an x-ray detector used for this purpose in the CT in most cases has a multitude of detector elements which generate the individual image pixels of a recording.
On account of the comparatively high energy of the x-ray photons to be detected, the high demands regarding the resolution to be achieved and the particular structural aspects especially with regard to compact design in a CT, for detection purposes the individual high-energy x-ray photons are converted by means of a scintillator by collisions in each case into a multitude of lower energy photons, for which now, on account of the lower energy, a spatially resolved detection is significantly easier within the scope of the mentioned restrictions. For this purpose the lower-energy photons are detected by means of photodiodes, and the photocurrents generated in the individual detector pixels are in each case measured by a current measuring apparatus, for instance an ASIC.
To measure the in most cases comparatively low currents which are generated in the photodiode pixels, ASICs of this type typically require one or a number of supply voltages, which results in a disadvantageously high total power consumption across the entire detector during operation due to the measurement of the photocurrents. Furthermore, direct voltages which are as stable as possible are desirable as supply voltages, as a result of which on account of the particular aspects of a CT, the emerging alternating voltage portions are complicated to filter when conditioning the supply voltages. On this account the typical procedure involves providing approximately the desired operating voltage of the ASICs from a high supply voltage by means of one or a number of direct voltage converters in a unit for voltage conditioning and in the process suppressing the alternating voltage portions in the unit on the output side by means of a corresponding filter. The individual ASICs are supplied with voltage in each case by the unit, wherein the voltage can be regulated to the correct operating voltage of an ASIC by the linear regulator in each case.
For this purpose due to the current load of the ASICs the output voltages of the unit must however be conducted in each case to the linear regulators by means of a high-capacity cable. The power loss is also high with the known solution.